Method and apparatus for making hollow plastic articles



June 27, 1950 R. E. ROBERTS 2,513,052

- METHOD APPARATUS FOR MAKING PLASTIC ARTICLES HOL Filed Dec. 11, 1945 4Sheets-Sheet l I A I ITOR. ROBERT ELDON ROBERTS IIIIIIIIIW 6 V J) a 4 fir/(w- June 27, 1950 R. E. ROBERTS 7 2,513,052

METHOD AP ATUS FOR MAKING I 1 HOL PL IC ARTICLES Filed Dec. 11, 1945 4 Sheets-Sheet 3 W MW 7 ROBERT ELDON ROBERTS.

m M uv June 27, 1950 1 R. E. ROBERTS 2,513,052

METHOD AND APPARATUS FOR'MAKING HOLLOW PLASTIC ARTICLES Filed Dec. 11, 1945 4 Shets-Sheet 4 INVENTOR. ROBE RT E LDON ROBERTS K? rc/ MQIVGZM Patented June 27, 1950 UNITED STATES METHOD AND APPAR T S FOR -Ame;

' HOLLOW'PLASTIC ARTICLE-S Robert Eldon Roberts, .Ridgefield Conn.- Applieation December 11, 19'45;SerialNo.- 634,259

25 Claims. 1

The object of invention is to provide a method and apparatus for quickly and cheaply forming hollow articles out of plastic sheet material. The invention .is well adapted, for instance, for iorming hollow rubber balls or bladders made of sheet rubber.

My method comprises in general the seating of sheet stock in cavities in a series of movable molds, the combined interiors of which are complementary to the exterior of the article to be made, and moving such molds into edge engagemerit to form a plurality of seams, thus making the complete article. In carrying out this method I provide a series of cavitary 'molds radiating about a center and having their cavities accessible for the seating of stock in the molds and I provide means for thereafterbr ing ing the various molds into edge engagement under pressure. My invention includes such method and apparatus broadly and .also more specifically :as hereinafter explained in connection -w ith--a preferred for-moi apparatus illustrated in the drawings.

In the-drawings, Fig. -1 is a sideelevation -partly broken away of a machine for making 'hollow rubber bal-ls by my method; this view showing the machine in=a closed position; Fig. 2 is-a plan of the top bed plate of such machine; Fig. '3 is a fragmentary vertical section through the top bed plate in the ofiset plane "indicated by the line 3-3 "on Fig. 2; Fig. his a vertical sec'tiono'f the forming portion of the machine in the open position; Fig. 5 is a plannf the :parts of the machine shown :in Fig. :4; Fig. '6 is a detail in cross section throughone of the molds and a portion of the frame, as indicated. by the line 6-6 in Fig. :5'; Fig. .7 jsra vertical sectionof the forming portion :of the apparatus :with the unolds in an intermediate .position, about midway between the open .and .closed :.positions; .Fig. 8 is a vertical section of a portion of the machine with {the molds in .closed position; Fig. :9 :is a;plan'.and Fig. 10 a verticalsection rof a suitable device employed in the apparatus :to deflect the {rubber between the molds; .Fig. .11 is a :cross section -:through the :four molds closed, as indicated :by the line l=l--:H in Fig. 8; Fig. :12 :isan enlarged xview illustrative of anyof the :four meeting edges :of the mold members illustrated in Fig. 11, and Fig. :13 :is aperspective of a ball :produced by the specific ,apparatus :shown.

'The'frame of myimachine .is::best shown inflig. 1,.1and comprises gar-base :Ill, :npright posts .1 and a ltop bed :p'late l2. Mounted on the :base H3 is accylinder 20 :to athe :heads 'of which are zsecured. conduits 2;! and :22- leading to wthe upper and 2 lower portion of the cylinder. Wit-hm the :cylinder is a piston 25 from which a piston rod :26 leads upwardly beyond the cylinder and :termiemates in a head 211 which operates the various molds. 1 Y

I have shown dour :molds 30 each having .a cavity 13!, the ssurzfiace :of which is .a meridional quarter of a..-sp'here, the tour molds being thus adapted by edge engagement :to define a sphere. That is to say, each of :the four radialimolds -30, in the particular -.embodiment shown, I make a .cavity which in the radial direction has .a semi? circleas its greatest dimension and in the trans!- verse direction a :quadrant, so that the four molds come :together the ,ldiametrically lope pos-ite points of the four molds will .all meetv at the poles of the sphere while in latitude .each cavity extend one-lquanter way around.

The 0111 molds 30 when open extend. horizon.- tal ly and mest on :thezbed. plate 12 of the machine. The moldsare :preferably triangular :on their .un..- der sides, as indicated :at .32 in Fig. 6, and-when open rest in radial grooves 13 the -bed iplate iii. The bed plate :is termed with a :centrahopene lfi'whichzis substantially square .withclts points toward lthe radialgrooves l3, .Withthe sidewalls flaring outwardly zand :cunving over .to. merge with lthe top, .as indicated at 3H5 in Figs. 3 :and-A.

The four molds 30,, resting .on the .bed I2.in

Fig. A, are =.c0nnected .a-titheir inner .ends :to-the head :21 on ctheoperating plunger 26 .by ;clevlises 35 .csecured to lthe inner ends of the molds and pivoted at 3 to the head c221. .lt results from this construction :that' when the piston rIOdlflB :is pulled downwardly from the position :shown :inzFig. =4, the imoldsare rocked inwardly toward eachlother through gradually :closing intermediate positions, one ofzwhich is shown iin Figuntil the molds come :into yentical position where they=coact with each cit-henaszshown 'inlliigs. 51 landia.

Briefly, therefore, in the operation of myiprocess, I seat rubber .ztas hereinafter described in detail) :in :the 1 diffierent H'XIOld cavities and admit fluid lunder :pressuretto the spine. 21! :at the upper portion of the cylinder to pull aldOWll'Ii'tl'l-G .piston rod, toswing the molds mto-lthe verticalvpositions shown in Fig. :1, thus joining theseated Portions to dorm a hollow sphere otsheetrubber.

Referrin now to A. A0 indicates a square open frame :having a roove 41 :in its ripper lface communicatin with -.a :nipple 42 for xthe attach: ment of a @vacuum conduit. movable-mom the rmachine land when removed to a.-.c.onvenient bench ;may have :a sheet :of rubber placed .onitopief it :andithe air exhausted :through f'Ihiskframe lis crethe nipple to seat the margin of the rubber in the groove, the intermediate portion sagging but being sustained across the open space.

The bed plate l2 of the machine is provided with four upright posts BB and when it is desired to operate the machine the frame 40 with a sheet of rubber clamped at the margin thereof and depending intermediately, as shown at R in Fig. 4, is placed on the posts so that the sheet of rubber extends over all of the four mold members. The vacuum is now released in the groove 4i and the sheet of rubber drops over the mold cavities with the four points of the square sheet outside the outer points of the four cavities. Each point of the sheet is then hooked downwardly manually onto a pin 38 projecting outwardly from each mold member. This anchors the sheet of rubber across the four mold members and over the piston rod head 21, then the frame 40 is removed.

When the sheet of soft raw rubber has been placed as described it sags to some extent into the four mold cavities and may be readily pressed manually vto a greater extent thereinto if desired. I now admit some compressed fiuid to the upper. portion of the cylinder pulling the piston. rod downwardly somewhat and rocking the molds approximately into the position in Fig. 7. With the molds in this intermediate position, I desire to seat the rubber accurately wardly in a suitable nipple or extension 53 for the attachment of an exhausting conduit. Accordingly, when the air is exhausted throughv these passageways the rubber extending across becomes accurately seated in each cavity, with very little stretching of the rubber.

I now take the device of Figs. 9 and 10 comprising a disc 60 having four upwardly and out wardly extending spring wires 6 I,-p1ace it on the central region of the raw rubber sheet, and push it down thereon if .necessary, until the rubber sheet is brought into contact with the-piston rod head 21, as shown in Fig. 7. The wires 6|, it will beunderstood, extend outwardly 45 to the molds,

and are thus midway between successive molds.

I now admit further compressed fluid through the pipe 2| to the upper part of the cylinder and swing the molds with the seated rubber into the vertical position shown in Figs. 1, 8 and 11. This brings the edges of thefour mold members into conjunction, the wires 6| holding the rubber sheet out of the way in the regionbetween the mold members, but with a light enough pressure so as not to pull the rubber across the rims of themolds.

, The edge of each mold member is formed into a V-shaped region, as shown in Fig. 12, and thus when the edges come together they act to pinch the projecting rubber on itself to form an eifective seam, and to pinch off the surplus rubber. This is illustrated in Fig. 12 where the rubber portions R at the inner side of two mold members are brought together and the part R. which projects outwardly between the members is pinched together by the edges of the mold formed into :an-eifective seam and the surplus out off, by the mutual pressure of the mold edges.

. .The ball, as illustrated in Fig. 13, is now completed and it is only necessary to release the each cavity. The passageway 50 terminates out 4. vacuum on the four mold cavities and admit fluid under pressure to the lower portion of the cylinder 20 to swing the molds into open position of Fig. 4 whereupon the completed ball is removed and placed in a spherical vulcanizing mold and vulcanized in the ordinary manner. The excess rubber and the diverting frame 60 are removed and the machine is ready to renew the forming operation when a fresh sheet of raw rubber is placed across the spread molds by the employment of the positioning frame heretofore described.

It will be seen that my machine is comparatively simple in construction and readily operated to manufacture at once a hollow rubber article formed out of sheet rubber by joining portions thereof by a plurality of seams. The article shown is a sphere and the seams produced are meridional seams through the poles in the form of two great circles at right angles to each other. For making other shapes of articles the cavities may be varied accordingly and the number of mold members may be varied, the different members, however, being so formed that each coaots with its neighbor to form a seam when'the members are brought into final closed position under pressure. 1

I claim:

1. The method of making hollow articles having opposed poles'from sheet material comprising placing such material across several cavitary mold members, each cavity extending from pole to pole and defining a fraction of the entire surface of the complete article, which fractions add up to one, and bringing said members toward each other to meet at the edges of the cavities to form a plurality of seams.

2. The -method of making ,a hollow rubber article comprising placing raw rubber stock in sheet form across several cavitary molds lying radially about a common center, the cavities being bounded by projecting cutting edges coming to a point at each end and thereafter swinging the molds toward each other to bring the edges of successive molds into coaction throughout their length to form a plurality of seams in the rubber.

3. The method of making a hollow sphere of plastic sheet material comprising arranging several cavitary molds in radial position about a center, each mold having a cavity which in its greatest surface dimension is longitudinally substantially a semi-circle and laterally a fraction of a circle defined by the numeral I over a numeral equal to the number of molds, seating the stock in such cavities and bringing the mold members togetherwhile holding back the sheet in a region between adjacent mold members to form a sphere having meridional seams extending from pole to pole.

- 4. The method of making hollow articlescircular in cross sectionfrom sheet material comprisin placing such material across several mold members, each having a cavity concaved longitudinally and transversely, bringing said members toward a common axis and causing the edges of adjacent cavities .to meet and form a plurality of seams. 5. The method of making round hollowarticles from sheet material comprising placing such material across several radiating mold members eachhaving a cavity concave longitudinally for one-half of-a perimeter'of the article andconcaved. transversely fora fraction of the perimeter of the article at right angles" to the per-im- 5 star 'flrst in-entioned, which fraction is ex-' pressed by the numeral l over the number, of molds, and bringing said mold members together to cause each to coact with two others or said mold members located respectively on opposite sides thereof to i'orm a plurality of seams.

6-. The method of making a Spherical article comprising placing asheet, 01' plastic stock across several cavitary molds, each cavity having a surface which is a section or a sphere and the cavities being bounded by projecting cutting edges, and thereafter moving the molds toward each other to bring the edges of adjacent molds into coaction to join the stock by a plurality of'seams.

7. The method of forming a hollow articlev of plastic material comprising placing such material in sheet form across a series of molds, each mold being provided with a cavity con'c'aved longitudinally and transversely, seating such stock within the cavities substantially in engagement with the surface thereof, and while the same is seated bringing the mold members into edge 'toedge coact'i'on to form a'plurality '1" seams.

8'. The method of forming a hollow article of plastic material comprising placing s'uch material in sheet form across a series of molds, each mold being "provided with a cavity complementary to a portion 'of the article to be produced, exhau'sting air from such cavities to seat the stock therein, bringing the mold members into edge to edge coaction to form a plurality of seams.

'9, The method of forming a hollow article of plastic material comprising placing such mate rial-in sheet form across a series of molds, each mold having a cavity which is concave both longitudinail'y and transversely and is surrounded by a cutting edge, exhausting air from the cavities to seat the sheet stock therein, bringing such mold members together into edge to edge coactie'n, each with two molds respectively on opposite sides thereof to form a plurality of seams;

10. The method of forming a hollow article of vulcanizable material, comprising placing a single sheet of such material across a series of molds radiating from a common center, each mold being provided with a cavity terminating in a surrounding cutting ridge, such cavity being complementary to a portion or the article to be produced, the sum of the cavities defining the entire exterior of the article, exhausting air from "such cavities to seat the stock therein, bringing the mold members into edge to edge coaction to form a plurality of seams, releasing the vacuum, and thereaiter removing and vulcanizing the article.

11. The method of making a hollow article from sheet stock comprising placing sheet stock across a series of cavitary molds arranged radially about a center, bringing the mold members into edge coaction while engaging the sheet in the regions between adjacent molds to positively hold back the excess of the sheet as the molds move into final position, the cavities of the set of mold members being formed to define the complete exterior of the article to be produced.

12. The method of making a hollow rubber article from sheet stock comprising placing sheet rubber across a plurality of cavitary molds arranged radially about a center, exhausting the air from the cavitie of the mold to seat the rubber therein, bringing the mold members into edge coaction while positively holding back the rubber sheet in the regions between edges of adjacent molds as they move into final position, whereby a closed article with a plurality of seams is formed.

iii

18'. The method of making a hollow rubber sphere comprising arranging four cavitary molds in radial position about a center, each mold having a cavity the surface of which is a fraction of a sphere extending longitudinally for substantially a semi-circle and laterally for substantially aduadra'nt, the edges of the cavities being defined by ridges extending about the cavities, placing a sheet of raw rubber over the Various cavities, seating the rubber sheet in each cavity by exhausting the air therefrom, and bringing the mold members together while holding back the rubber "sheet in the regions between adjacent mold members to join the rubber by meridional seams extending from pole to pole and located apartat the equator and pinching off the surplus stock and finally vulcanizing the product.

14. apparatus for'forming hollow articles of plastic 'sheet material comprising a set of cavitary molds, the cavity in each mold being concave longitudinally and transversely and coming to a point at each end, means for supporting the molds so that sheet material maybe placed over the cavities, and means for moving the molds toward each other to bring each into edge 'coaction with two others of the molds for the entire boundary 'of the cavities to join the material by a plurality of meridional seams.

15; -.;An apparatus for making hollow spheres of plastic sheet material comprising several cavitary molds arranged in radial position about a 'center, each mold having a cavity which in its surfacedimensi'on is longitudinally substantially a "semi circle and laterally a fraction of a circle defined by one *over a numeral equal the num'ber'of molds, and mechanism for swinging said molds to "cause their edges to come into contact throughout the length of the cavity and thereby form a plurality of meridional seams extending from pole to pole of the sphere.

16. An apparatus for making hollow articles of plastic sheet material comprising a set of cavitary molds arranged radially about a center, and means for moving the molds to bring each into edge 'coaction with two "others of the molds, each mold having a cavity which is concave longitudinally and transversely and *is such a section of the complete article that when the molds are broughtto'gether their cavities enclose the complete article.

i7. apparatus for forming hollow articles of plastic material comprising a set of cavitary molds, the cavity of each molding surface forming a fraction less than half of the entire article, and the -sum of the cavities presenting a surface defining a complete closed article, means for supporting the molds in a radial position about an axis, means for exhausting the air from the cavities of the molds to seat stock therein and means for rocking such molds to bring them from stock-receiving position into edge coaction to form a plurality of seams in the article.

18. An apparatus for forming hollow articles having opposed poles from sheet material comprising a set of molds extending radially from a center, each mold havin a cavity extending from pole to pole of the article, an operating member at the center to which the molds are pivotally connected back of the inner point of the cavity and means for guiding the molds when they are shifted by the operating member, whereby the molds may be rocked from a spread position into a coacting position of their entire edges.

19. The combination of a frame, a series of aaragoas frame, and guiding meansv extending. inwardly and downwardly and engaging the underside of the molds, whereby said downward movement of the inner ends results in the rocking the,molds inwardly to bring them into edge coaction. 20.-T he combination of a frame having a bed plate with an opening in it, a. set of cavitary molds adapted to rest on the top of the bed plate in radial positions about said opening with the cavities facing upwardly, and means for moving the inner ends of the molds downwardly into the opening in the bed while the bed supports the :molds and the edges of said opening form guides :alOIlg which the molds may traveLthereby rock-.-

:ing the molds with the stock toward each other :until the molds come into edge engagement.

21. The combination of a frame having a bed plate with an opening through it, a set of caviitary molds adapted to rest on .the bed plate in radial positions about the opening with the cav ities facing upwardly, an operating deviceadapted to extend into the openin and pivotally connected to the molds below the entrance to the inner ends of the cavities, means for seating sheet stock above the molds in the cavities thereof, and means for actuating said operating device to move the inner ends of the molds downwardly into the opening in the bed while the edges of said opening form guides along which the molds may travel, thereby rocking the molds with the stock seated in the cavities toward each other until they come into edge engagement.

22. In an apparatus for forming hollow articles of plastic sheet material, the combination of a series of cavitary molds extending radially about a center and adapted to have a sheet of stock placed across their open faces, means for moving the molds to bring them into edge coaction, and means engagin the sheet of stock outside of the .cavities for holding back the excess of the sheet of stock in the regions outside of the cavities and between adjacent molds.

' 23. The combination of a series of molds ar-' ranged radially about a center, means to support the molds with cavities therein facing upwardly, whereby sheet material may be placed over the cavities, a sheet holdingdevice having as many upwardly and outwardly extending arms as there are molds, means for supporting said device at the center-and above the sheet stock with the armsuextending betweenmolds, and means for: making the molds as a unit to. bring them into coaction,.while said device holds back the sheet of material between the molds as they comeinto.

coaction.

2i. .'Ihev combination of a frame havmga bed plateiwith an. opening therein, a setof .mplds with .upwardlyfacing cavities, said molds. being adaptedlto rest on the bed plate in a radial .posi. tion about a center and receive sheet material intheir. cavities and means for moving. down-.

wardly and inwardly the inner ends of .the. molds,

intothe opening of the bed plate .to cause the edgesto coast with each other to form ahollow rubberarticle'joined by meridional seams, anda sheet holding device having upwardly and out-e, wardly extending .members to hold back-, the sheet between the molds. 25.v Anapparatus for making. hollow/rubber spheres comprising a frame having a bed plate withan opening therein, a set of four equidise tant. molds with upwardly facing cavities, each cavity being complementary to one-fourth of a sphere, said molds being adapted to rest on the bed plate in a radial position about -a center, means for attaching a sheet of rubberto. the molds over the cavities, means for. exhausting the air from the cavities to seat the rubber therein, .a.. cylinder, a. pistontherein having a rod with a head pivotally connected with the in.- ner. ends ofth'e. molds for moving them'.downwardly into the opening of the bed plate to rock the .moldsinwardly and their edges to coact with eachother to form a hollow rubber article joined .by...meridional seams, and a holding device formed for .mounting on rubber stock .over the piston head. and having four upwardly and cute wardly extendin members projecting between themolds to hold back the rubber between'the molds.

ROBERT ELDONROBERTS.

I REFERENCES CITED The following references are of record in the filed this patent:

UNITED STATES PATENTS Number Name Date "T 637,372 ICox Nov. 21,1899 1,270,873 Robertson July 2, 1918 1,467,438 Lawton Sept. 11, 1923 1,497,592 Roberts June 10,1924 1,639,430 Gammeter Aug. 16, 1927 2,229,613 Strauch Jan. 21, 1941 

